Medical errors are a critical public health risk and are largely avoidable. Although hospitalized children suffer from three times the rate of potentially dangerous medical errors compared to adults, many interventions 3roposed to reduce hospital errors have not been evaluated in children. One intervention proven effective in adult patients is the use of computerized physician order entry systems (CPOES). CPOES reduce inpatient medication errors by 55%. Three more than half of the nation's hospitals are planning to implement CPOES in the future. The effect of these systems on errors in hospitalized children has not been well described. Since children suffer from different types of inpatient errors than adults, it is conceivable that the effect of CPOES in children may be different. In addition, the impact of CPOES laboratory menus and alerts on the volume of inpatient laboratories ordered has not been described. This information is important to lab resource allocation and quality control during implementation of CPOES. Lastly, whenever a new system is implemented at a hospital, new errors are expected to occur. The types of new errors that emerge with implementation of CPOES have not been studied. The aims of this study are: (1) to evaluate the effect of CPOES at Boston Medical Center (BMC) on the number of medication errors in the inpatient pediatric wards; (2) to qualitatively describe changes in the types of pediatric medication errors after the implementation of CPOES; and (3) to measure changes in laboratory ordering practices before and after the implementation of CPOES. The change in slope of errors over time will be measure in order to account for a baseline declining rate of medication errors at BMC. The success of this proposed study will help those hospitals investing in CPOES understand its impact on children. Information on new types of errors will allow hospitals implementing CPOES to take measures to prevent or reduce these errors in the future.